Star Trek loves itself a Cave episode. You can do a bunch of different stories in similar looking sets, you can restrict which members of the cast are the focus, you can thrust unlikely pairings together and force them to bounce off each other. Caves are good! Lower Decks not only agrees with this, but uses what is usually a limitation in live-action to delivery a really important episode for its heroes.As the name implies, “Caves” sees Boimler, Mariner, Tendi, and Rutherford all stuck in a cave during an away mission. Unable to communicate with the Cerritos and their cave slowly filling with unstable moss, the isolation forces each of the team to reflect on prior times they got stuck in a cave during an away mission, because that’s really just a good 30% of a Starfleet officer’s career.These anthology-formatted flashbacks, save for Tendi’s—which is important for a different reason we’ll get into later—all crucially isolate each member of the main cast from the rest of them. Instead, they’re either dealing with superior officers, like Rutherford and Dr. T’Ana (who get stuck in a cave and deal with another classic Trek trope, the forced alien pregnancy) in his story, or in the case of Mariner and Boimler, leveraging their newfound promotions to see them having to take the lead as senior officers to other colleagues.In true cave episode style, these lean on that aforementioend beloved Trek scenario of flinging unlikely pairings together to create conflict to overcome. Rutherford’s usual passive persona forces him to step up to the occasion when forced to survive with the irascible Dr. T’Ana, while Mariner has to overcome her prejudices for the Delta Shift Cerritos crew she’s leading during a prior crash landing, and Boimler has to spend time with a conspiracy theorist he cannot stand. They’re all funny ideas individually, but together they represent just how much our ensigns have evolved over the course of the show—not just in becoming Lieutenants and having more responsibilities, but how they’ve matured as people to deal with situations like this. All three of these situations are ones where previously Rutherford, Mariner, and Boimler would’ve miserably struggled with. Rutherford being bowled over by Dr. T’Ana, Mariner unable to get past her pre-judgmental attitudes and work with others, Boimler confronting literally anyone he can’t people-please: all of these would’ve been situations that completely undid them previously, and often to hilarious effect. But Lower Decks has changed, and these characters have along with it, and instead we get to see them all adapt to these situations and overcome them instead.This is smartly contrasted with Tendi’s own cave story, which isn’t really a cave story at all. It’s a sibling to the trope—being stuck in a turbolift instead of a cave—but it’s important not just as the only flashback to feature all four main Lower Decks stars together, but takes us all the way back to the very first episode of the show to see how their bond formed in the first place. It’s bittersweet, to watch the early days of their friendship form, when put up against tales where each of them are now apart from each other, driven by the trajectory of their careers. But it further re-inforces that Mariner, Boimler, Tendi, and Rutherford’s bond is in fact stronger than ever in the here and now: they don’t have to be together to embody the lessons they’ve learned as friends, they don’t need to be directly by each other’s side to bring out the best in themselves. Each of these four characters have now had time to grow and change as people over Lower Decks’ four seasons to the point that they can each handle being on their own sometimes—knowing that their friends will always be there for them at the other side of every duff cave away mission.It’s a sweet, smart leverage of a legendarily silly Star Trek trope—one often delivered as a way to scrimp and save on the budget. Here, Lower Decks enriches the cave format by bring out the very best of what it can do from a character perspective. And given “Caves” positioning as the last episode before Lower Decks’ typical two-episode endgames for a season, it’s a fitting moment to look back on how far these characters have come... before they undoubtedly face a trial that will challenge them unlike anything they’ve faced before.Star Trek: Lower Decks is available to stream now on Paramount+ Want more io9 news? Check out when to expect the latest Marvel, Star Wars, and Star Trek releases, what’s next for the DC Universe on film and TV, and everything you need to know about the future of Doctor Who.